Primordial Magic creates many forms of matter. This has the potential to greatly affect the world around the magician. However, this matter only exists for a short while, eventually dissipating into the same nothing it came from. This process releases the energy of the matter back into the environment. This process is called radiation, as each particle decays and radiates away.
Unfortunately for primordial mages, this can negatively impact the environment. The exact reason is a subject of debate among the more scholarly mages, but the result is that sometimes, things go awry. Older mages have been known to grow tumours, lose their hair or even more radical things - including death. In addition, sometimes spells go wrong and instead of simply fizzling, create an anomaly.
In game terms, this is represented by an instability score. One of the side effects of an newly inscribed spells can be to increase your instability score. If your instability score reaches 10, you should contact a GM. Instability cannot be reduced.